Endometrial thickness of less than 7.5 mm is associated with obstetric complications in fresh IVF cycles: a retrospective cohort study.

RESEARCH QUESTION:Does endometrial thickness affect the occurrence of obstetric complications in fresh IVF cycles? DESIGN:We conducted a retrospective cohort study that included all singleton deliveries resulting from fresh embryo transfers in a single centre between 2008 and 2014. Obstetric complications, i.e. preeclampsia, placental abruption, placenta previa, small for gestational age and preterm delivery, in singleton live births were compared among patients with an endometrial thickness of less than 7.5 mm and 7.5 mm or over on day of HCG triggering. We adjusted for confounders, including maternal age, body mass index, smoking, peak oestradiol, parity, chronic hypertension, pre-gestational diabetes, gestational diabetes, vanishing twin, inherited or acquired thrombophilia, and past pregnancy complications. RESULTS:A total of 5546 fresh embryo transfer cycles were carried out during the study period, of which 864 singleton deliveries met inclusion criteria. After adjusting for potential confounders, an endometrial thickness of less than 7.5 mm was found to be associated with increased risk for adverse obstetric outcome (adjusted OR 1.53; 95% CI 1.03 to 2.42; P = 0.04) even after excluding patients with prior pregnancy complications (adjusted OR 2.2; 95% CI 1.05 to 4.59; P = 0.035). CONCLUSIONS:Our results demonstrated that a thin endometrial lining was associated with obstetric complications that might be related to poor placentation. These findings should be validated in large prospective cohort studies.